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4 September 2008 Adsorption of mercaptosilanes on nanocrystalline and single crystal zinc oxide surfaces
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The wide band gap and unique photoluminescence (PL) spectrum of nanocrystalline zinc oxide (nano-ZnO) make it attractive for a variety of photonics and sensor applications. Toward the goal of modifying the electronic structure and optical properties of nano-ZnO, the adsorption of 3-mercaptopropyltriethoxysilane (MPTES) has been investigated. Nano-ZnO rods having widths of 10-20 nm and lengths of 100-300 nm were functionalized by ultrasonicating them in a hot ethanol/water solution and adding MPTES. FTIR and X-ray photoelectron spectroscopy (XPS) of the modified nano- ZnO confirm silane functionalization. The presence of hydroxyl groups prior to functionalization suggests that adsorption to ZnO occurs primarily via a condensation reaction and the formation of Zn-O-Si bonds. Comparison has been made to 3-mercaptopropyltrimethoxysilane (MPTMS) adsorbed in ultrahigh vacuum onto sputter-cleaned single crystal ZnO(0001) in which MPTMS vapor is leaked into the vacuum chamber. In this case, bonding occurs via the thiol groups, as indicated by angle-resolved XPS studies. Similar experiments in which sputter-cleaned ZnO(0001) is dosed with dodecanethiol (DDT) confirm adsorption via S-Zn bond formation. Photoluminescence measurements of MPTES-functionalized nano-ZnO show an increase in intensity of the UV emission peak and a decrease in the visible peak relative to the unfunctionalized particles. The reduction of the visible emission peak is believed to be due to passivation of surface defects.
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Jagdeep Singh, JiSun Im, James E. Whitten, Jason W. Soares, Alexa M. Meehan, and Diane M. Steeves "Adsorption of mercaptosilanes on nanocrystalline and single crystal zinc oxide surfaces", Proc. SPIE 7030, Nanophotonic Materials V, 70300T (4 September 2008);

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